I want to answer a past exams question with a clean/simple way about:
Why does ATM protocol use for virtual circuit numbering both VPI and VCI logical numbers?
From what I've understood: The VCI changes through the nodes that it goes through and VPI has the destination path.
I found this also: The address is broken into a VCI and a VPI subfield. Session following the same path for several nodes can be assigned the same VPI. Some switches only look at VPI, simplifying switch complexity.
Can someone help me get this cleared?